"They will meet" on the sidelines of the G-20, Putin spokesman Dmitry Peskov told reporters Thursday, but he added: "If we are speaking about preparations for a separate meeting with Trump, no preparations are being made for any separate meeting at the moment".
National security adviser HR McMaster said that the high-stakes meeting with Mr Putin is among several scheduled for when Mr Trump is in Hamburg next week.
Trump has long played down reports of Russian meddling, but he seized on recent reports about former president Barack Obama's cautious reaction to election interference previous year to attack Obama for a timorous response.
"It appears that they took the warning seriously", Mattis said, referring to the regime of Syrian President Bashar al-Assad, saying it had not launched any new chemical attacks.
"We have no specific agenda", Mr McMaster said during a briefing on the trip, which includes a stop in Warsaw.
Since Trump's inauguration, he and Putin have shared three phone calls.
In the midst of the 2016 election, self-described whistleblowing organisation Wikileaks uploaded a tranche of emails that were stolen from the account of Clinton's campaign manager John Podesta, including many that embarrassed the then-frontrunner.
Mr Trump and his administration have repeatedly denied any collusion with Moscow, with Mr Putin also denying any hacking on behalf of Russian Federation.
"It's whatever the president wants to talk about", McMaster said. Russian Federation denies the allegations and Trump says his team did not collude with Moscow.
Russian Foreign Minister Sergey Lavrov has already warned "master of the deal" Trump that "Putin also knows how to negotiate, and does it always in the interest of Russia". Such concessions could include returning two diplomatic compounds in the U.S. to Russian Federation or lessening sanctions.
"Our relationship is at an all-time low, and it's been deteriorating further".